1. Field of the Invention
The present invention is concerned with oriented polyacrylonitrile films which have been coated on one or both sides with a vinylidine chloride multipolymer coating composition.
2. Description of the Prior Art
In the past thermoplastic and thermoset packaging films such as for example polyolefin films including polyethylene and polypropylene and polybutene and copolymers thereof; polyester films such as for example polyethylene terephthalate and the like have been coated with a variety of coating compositions including vinylidine chloride multipolymers to improve the heat sealability thereof as well as improving resistance of such films to oxygen and moisture vapor penetration thereof. In the past when such film materials have been coated with saran latexes having high concentrations of vinylidine chloride contained therein, and when such films were sealed and exposed to high moisture concentrations such as for example immersion in water at room temperature or above, there was a tendency of the seal to fail by delamination of the coating from the film substrate. This is particularly true in the case of saran coated polyacrylonitrile films. Prior art saran coated film structures have been described in the prior art, see for example U.S. Pat. Nos. 3,617,368 and 4,058,649.
In general, saran coating systems which have been used in the past comprise saran coatings which are commercially available in the form of latexes which are to be applied to the particular film substrate from an aqueous media. A latex, by definition, is a dispersion of spherical, polymeric particles in a range from about 0.01 up to about 1.0 micron (0.004-0.04 mils) diameter in water. Latex coating systems employed for coating applications to film substrates generally consist of from about 50% to about 60% solids with about 2% to 3% of the solids being conventional, wetting and suspending agents. On drying the applied coating, the water evaporates and the particles fuse together at their contacting surface.